Akira Adachi

Multilayer electroluminescent device using organosilicon polymer as hole transport layer

Abstract Double-layer-type organic electroluminescent devices using organosilicon polymers, such as poly [4,4′-(1,2-dimethyl-1, 2-diphenyldisilan-ylene)-phenylylene], poly [4,4′-(1,2-dimethyl-1,2-diphenyldisilanylene) -biphenylylene], poly[(1,2-dimethyl-1,2-diphenyl-1, 2-disilany-lene)-1,5-naphthylene] and poly [(1,2-tetraethyldisilanylene)-9,10-anthracene] (PDEDS-AN), as hole transport layers were fabricated. In these devices, tris(8-quinolinolato) aluminum(III) complex (Alq) was used as an electron-transporting emitter layer and the effect of the π-electron system of the polymers on device performance was investigated. Among the devices, the PDEDS-AN-based device exhibited the highest external quantum efficiency (QE) of about 0.2%. The low QE values of the organosilicon-based devices compared with that (0.8%) of the double-layer-type device having poly( N -vinylcarbazole) as a typical hole transport layer may be attributed to the poor electron-blocking properties of the organosilicon polymers.

Synthesis and properties of alternating polymers containing 2,6-diaryldithienosilole and organosilicon units

Nickel-complex-catalyzed dehalogenative coupling of diGrignard reagents prepared from bis(bromoaryl)disilanes or monosilane with 2,6-dibromodithienosiloles afforded the corresponding polymers composed of alternating 2,6-diaryldithienosilole and organosilicon units. These polymers exhibit strong UV-vis absorption and emission bands at 422–444 and 482–541 nm, respectively. Their cyclic voltammograms display the first oxidation peaks at 0.95–1.00 V vs. SCE (saturated Calomel electrode). When the polymer films were doped with FeCl3 vapor, the films became conducting, and their conductivities were determined to be 3.3×10–5 – 8.7×10–3 S/cm using the four probe method. Electron- and hole-transporting properties of the polymers were also studied by evaluating the performance of electroluminescent (EL) devices based on these polymers.

Synthesis of novel bithiophene derivatives with an organosilanylene bridge, and their applications to electron-transporting materials in EL devices

Compounds having two bithiophene units linked by an organosilicon bridge were prepared. Their UV spectra and cyclic voltammograms indicated that the compounds have the low-lying LUMO. The electron transporting properties of the present silicon-bridged bithiophene derivatives were evaluated by the performance of electroluminescent (EL) devices having vapor deposited silicon-bridged bithiophenes, Alq, and TPD layers, as the electron-transport, emitter and hole-transport, respectively. By applying the bias voltage on the devices, the devices emitted green EL originated from the Alq emission with the maximum luminance of 8500 cd m−2.

Synthesis and properties of silicon-bridged bithiophenes and application to EL devices

Dithienosiloles (DTSs) were prepared and their optical and electrochemical properties were examined in view of electron-accepting ability of them, in comparison with the results of theoretical calculations. They were found to have low-laying LUMOs, and an EL device with pyridyl-substituted DTS as the electron-transporter exhibited high efficiency of current-luminance energy conversion.

Effect of UV irradiation on polypyrrole as studied by electron spin resonance

Abstract The effect of UV irradiation on polypyrrole (PPy) doped with benzene sulfonate has been investigated by electron spin resonance (ESR). In this paper we examine the changes in the ESR spectrum parameters, i.e., peak-to-peak linewidth, asymmetrical parameter and spin concentration, referring to the change in the PPy conductivity. During UV irradiation, the linewidth of the ESR spectrum increased, probably due to the production of localized spins when the scission of the polymer chains starts to occur. After UV was switched off, the linewidth reverted to its initial value due to the re-unification of the polymer structure. Using high intensity irradiation, the spin concentration gradually decreased, probably due to the rearrangement of the polymer structure. This seemed to induce a decrease in the kink of the polymer, that is, a decrease of both polarons and bipolarons. The decrease of polarons is therefore related to the decrease of the relative spin concentration, and the decrease of bipolarons induces the degradation of the PPy conductivity.

Electron spin relaxation studies of conducting polypyrroles : The difference of the relaxation processes between highly conducting and semiconducting polypyrroles

Abstract The properties of electron spins in highly conducting ( σ = 50 S cm −1 ) as well as in semiconducting ( σ = 10 −2 S cm −1 ) polypyrroles are investigated on the basis of the electron spin relaxation times ( T 1 and T 2 ) measured with pulsed EPR. The temperature dependence of T 1 and T 2 in the good conductors is explicitly different from those in semiconductors. Redfield theory of spin relaxation, applied in order to evaluate the difference, makes it possible to estimate the correlation times and the fluctuating local fields for the two types of polypyrroles. The spin correlation time of good conductors is much shorter than that of semiconductors, a fact that apparently demonstrates that the electron spins in PPy move more rapidly with increasing conductivity. Also the local field in semiconducting PPy is found to be constant over the whole temperature range, while the good conductors exhibited an increasing local field with increasing temperature.